1. Field of the Invention
The present invention relates to a method for detecting strength of receiving signals of users in a code division multiple access(CDMA) system, and more particularly, to a method for detecting strength of received signals of users in a code division multiple access system, which can upgrade a service quality for users and improve system performance by detecting strength of received signals received from a base station in a code division multiple access cellular system.
2. Description of the Related Art
In general, a method for detecting strength of received signals of users in a code division multiple access system is one of the important technologies required for analyzing and testing signal characteristics in a code division multiple access system. However, no effective method for detecting strength of received signals of users in a code division multiple access system has been proposed even in any of industrially advanced nations as of today. Hence, a need exists in the art for an improved method for detecting strength of received signals in a code division multiple access system.
In the code division multiple access system using a Spread Spectrum(SS), the capacity of radio links varies depending upon interference amounts contained in the radio links even in the same bandwidth as opposed to a frequency division multiple access(FDMA) system or a time division multiple access(TDMA) system. Generally, the capacity of the backward link(i.e., radio link from the terminal to the base station) is smaller than that of the forward link(i.e., radio link from the base station to the terminal), the capacity of the radio links for the code division multiple access system is determined in accordance with the capacity of the backward link. For example, assuming that if the service quality can be represented as Signal-to-Noise(S/N) rate(Eb/No) and the rate value is 7 dB the capacity(N) of the radio links for the code division multiple access system according to IS-95 in which the bandwidth is 1.2288 MHz and the signal speed processed by one user can be expressed by the equation (1) as follow: ##EQU1##
However, the actual capacity of the radio links for the code division multiple access system is affected by various factors, i.e., voice activity, background noise and sectorization effect and so on in addition to the above factors. Especially, the interference received at the base station is arrived from not only the user's cell but also the external user'cell, and this interference amounts from external cell is varied depending on the external conditions, i.e., the radio propagating characteristics and the size of the hand-off area, etc. If the interference amounts from the external decrease, the actual capacity of the radio links for the code division multiple access cellular system increases. In contrast to the above, if the interference amounts from the external increases, the actual capacity of the radio links for the code division multiple access cellular system decreases. Therefore, in the code division multiple access cellular system, the signal power received from the users is strictly controlled in order to increase the capacity of the radio links. Consequently, to detect and analyze the receiving signals from the users is an important role in increasing the capacity of the code division multiple access cellular system.
However, no method has been proposed to immediately detect the received signals transferred from the users,till now. The measurements of the service quality is being made only using a bit error rate of the receiving signals. In the system where the receiving power of the users is controlled, a bit error rate of the received signals remain almost uniform. If a bit error rate of the receiving signals is uniform, strength of the received signals to total interference amounts rate also become uniform. Thus, there is a problem that the presently used measurements of the bit error rate of the received signals can test the performance of the power controlled system only in part and can not be applied to test the characteristics and performance associated with the individual users including the radio links. Further, there is a drawback that the performance of the entire system cannot be tested.
It is therefore an object of the invention to provide a method for detecting strength of received signals of users in a code division multiple access system, which can upgrade a service quality for users and improve system performance by detecting the received signal strength in a code division multiple access system.